linux-kernel - Re: [RFC] perf/core: what is exclude

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Date:   Fri, 20 Apr 2018 12:51:12 -0400 (EDT)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     Vince Weaver <vincent.weaver@...ne.edu>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Stephane Eranian <eranian@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>, mingo@...e.hu,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [RFC] perf/core: what is exclude_idle supposed to do

On Fri, 20 Apr 2018, Vince Weaver wrote:

> > AFAICT it works on Power and possibly ARM.
> 
> at least some ARMs are a bit more honest about it than x86
> 
> ivybridge:
> 	Performance counter stats for '/bin/ls':
> 	1,368,162      instructions
> 	1,368,162      instructions:I
> 
> pi2/ARM cortex-A7
> 	Performance counter stats for '/bin/ls':
> 	1,910,083      instructions
> 	<not supported>      instructions:I
> 
> I'd fire up my Power8 machine to see but not sure it's worth the hassle 
> and/or having to get out the ear protection.

I did power up the Power8 machine in the end:

power8:
	perf stat -e cycles,cycles:I sleep 5
	Performance counter stats for 'sleep 5':
        14,271,273      cycles
        14,271,273      cycles:I

???

But then if I try again on power8

	perf stat -a -e cycles,cycles:I sleep 5
	 Performance counter stats for 'system wide':
	1,238,772,322,327      cycles
 	1,238,674,771,713      cycles:I   

there is a difference.

But then on ivybridge

	perf stat -a -e cycles,cycles:I sleep 5
	Performance counter stats for 'system wide':
	589,598,104      cycles
	589,537,190      cycles:I

there is also a different in system wide mode.

So maybe exclude_idle does do something on x86?  Or am I completely 
misunderstanding what the flag is supposed to be indicating?

Vince